Repetitive keyer actuating circuit for an electrical musical instrument

ABSTRACT

In an electrical musical instrument of the keyboard type having a plurality of selectively played keys for connecting corresponding tone generator keyers to a source of keying voltage, a repetitive keyer actuating circuit operable in response to key playing to produce electrical keying pulses for alternately and repeatedly actuating two sets of keyers. The repetitive keyer actuating circuit comprises a keying pulse generator in circuit with the voltage source and the keys and operable in response to key playing to alternately and repeatedly provide at each of two outputs keying pulses at regular preselected time intervals, and keying pulse sustain circuits each in corresponding circuit arrangement with one of said outputs and a set of keyers and operable to produce multiple stage envelope decay for said keying pulses. Each set of keyers is actuated by an initially percussive and subsequently sustained keying pulse to provide musically satisfactory repeatable effects throughout the range of keying pulse frequencies.

United States Patent 1191 I 1111 a Schreier June 2, i974 REPETITlVE KEYER ACTUATING CIRCUIT Primary remnant/India. i i/111516561 FOR AN LECTR CAL MUSICAL Assistant ExaminerStanley J. Witkowski INSTRUMENT Attorney, Agent, or Firm-Lowell C. Bergstedt [75] Inventor: Wilford R. Schreter, Bensenville, Ill. ABS H CT In an electrical musical instrument of the keyboard type having a plurality of selectively played keys for [73] Assignee: Hammond Corporation, Deerfield,

Ill. 4

[22] Filed: .lune Ill, 1973 connecting corresponding tone generator keyers to a source of keying voltage, a repetitive keyer actuating [21] Appl' circuit operable in response to key playing to produce electrical keying pulses for alternately andrepeatedly 52 us. c1 84/118, 84/126, 84/DIG. 23 actuating two Sets of y The repetitive keyer [51] int. Cl. Gloh 11/02 mating circuit prises a keying pulse generator in [58] Field 61 Search 84/1.01, 1.13, 1.24, 1.26, eireuit with the voltage Source and the y and p g4/DIG 2 DIG 12 DIG 23 able in response to key playing to alternately and ree u peatedly provide at each-of two outputs keying pulses at regular preselected time intervals, and keying pulse sustain circuits each in corresponding circuit arrangel References Cited ment with one of said outputs and a set of keyers and UNITED STATES PATENTS operable to produce multiple stage envelope decay for 3,476,864 11 H969 Munch 84/DIG. 2 Said keying P Each Set Of keyers is actuated y 3,493,668 2/1970 Bunger an initially percussive and subsequently sustained key- 3,526,702 9/1970 Freeman.... ing pulse to provide musically satisfactory repeatable 3,627,895 12/1971 Savon effects throughout the range of keying pulse frequen- 3,67l,659 6/1972 Suzuki 84/l.l3 X ie l0 Claims, 5 Drawing Figures PULSE REPEAT PULSE Q moves 22 OSCILLATO AMPLIFIER I 5 57 KEY-DOWN 23 DETECTOR 72 19 l 6| "K 76 '13 REPEAT 'w 3 Jl DR'VER SUSTAIN l7 cmcun E AND |4VOLTS MPLIFIER aa- KEYING BUS 4-TTT-0oo" 1 K I OTHER R IE 'Z 1e KEYING 1, ONE VOLTAGE I KEYER KEYER REPEAT E 19 b 119 1 l KEYER ER OTHER I OUTPUT I g gpu :NON- TONE 1 EPEAT SIGNAL 1 SOURCE 1 f SOURCE a SELECTOR SWITCH REPETITIVE KEYER ACTUATING CIRCUIT FOR AN ELECTRICAL MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electric circuits for use with an electrical musical instrument of the keyboard type such as an electronic organ and operable in response to key playing to produce electrical keying pulses for repeatedly actuating known electronic tone generator keyers.

2. Description of the Prior Art In an electrical musical instrument of the keyboard type such as an electronic organ having a plurality of selectively played keys for connecting known electronic tone generator keyers to a source of keying voltage, it is frequently desirable to provide in response to key playing repeating percussive keying pulses for actuating tone generator keyers in order to produce a pleasing musical effect. Repetitive keyer actuating circuits for accomplishing this result generally include means for producing percussive keying pulses for alternately and repeatedly actuating certain tone generator keyers which gate to an output tone signals corresponding to musical instruments such as the Xylophone and marimba, for example, which are typically played with plural mallets. It is important that the keying pulses are provided at regular and equal time intervals, which are generally preselected by varying the frequency of an oscillator typically included within such a repetitive keyer actuating circuit.

Prior systems known to applicant for providing repetitive keyer actuating pulses all have the common disadvantage, as those familiar with electrical musical instruments will appreciate, that, as the frequency of the keying pulses is varied, a complicated adjustable or sliding resistor-capacitor time constant output circuit for correspondingly and accurately varying the keying pulse waveform envelope decay is desirable in order to provide musically satisfactory repeatable effects. If such a sliding time constant output circuit is not provided, percussive keying pulses produce musical tones sounding tooshort to provide a pleasing musical effect at slow pulse frequencies; as the sustain time is increased through the use of fixed resistor and capacitor combinations having larger time constants, the rate at which the musical tone can be repeateddecreases if its percussive character is to be retained. The sliding time constant circuit requires a difficult and accurate simultaneous adjustment of the frequency of the repeating pulses and the time constant of the pulse output circuit for each set of keyers, which, in practice, requires considerable complexity.

SUMMARY OF THE INVENTION The present invention overcomes these shortcomings of prior systems known to applicant for producing repetitive keyer actuating pulses. The repetitive keyer actuating circuit according to the present invention provides musically satisfactory repeatable effects throughout the entire range of keying pulse frequencies without the need for a sliding or adjustable time constant circuit.

In general, in an electrical musical instrument of the keyboard type having a plurality of selectively played keys for connecting tone generator keyers to a source of keying voltage, the repetitive keyer actuating circuit according to the present invention is operable in response to key playing to produce electrical keying pulses for alternately and repeatedly actuating two sets of keyers. The repetitive keyer actuating circuit comprises a novel keying pulse generating means in circuit with the voltage source and the keys and operable in response to key playing to alternately and repeatedly provide at each of two outputs keying pulses at regular preselected time intervals, and keying pulse sustain circuits each in corresponding circuit arrangement with one of said outputs and a set of keyers and operable to produce multiple stage envelope decay for said keying pulses. Each set of keyers is actuated by an initially percussive and subsequently sustained keying pulse. The keying pulse sustain circuit comprises the subject of a separate co-pending application Ser. No. 368,878, filed on June 1 l, 1973 in my name entitled SUSTAIN CIR- CUIT FOR PRODUCING MULTIPLE STAGE ENVE- LOPE DECAY and which is assigned to the same assignee of record as the present application. Briefly, however, this sustain circuit is operable to produce for each keying pulse an initially percussive or rapidly decaying pulse waveform envelope (first decay stage) which allows fast repetition of sustained musical tones while still maintaining their percussive character and a subsequently sustained or more gradually decaying pulse waveform envelope (second stage) which enables the desirable sustained musical effect at slower repeating pulse frequencies.

The circuit according to the present invention also includes means for eliminating the undesirable effects of key bounce, which is frequently useful for use with electrical musical instruments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a block diagram illustrating the basic features of the preferred embodiment of the present invention;

FIG. 2 is a schematic diagram of the pulse generator and key-down detector illustrated in FIG. I;

FIG. 3 is a schematic diagram of the repeat oscillator shown of FIG. 1.;

FIG. 4 is a schematic diagram of a typical driver or output stage utilized in FIG. l; and

FIG. 5 is a schematic diagram illustrating a typical sustain circuit and amplifier also included in the circuit of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the preferred embodiment of the present invention which is illustrated in block diagram form in FIG. 1, a keying bus 10 is shown connected to a voltage source at terminal ll through a lead 12, a pulse generator 13, a lead 14, a key-down detector 16 and a lead 17. Terminal II is in turn connected to a supply having a voltage of 28 volts, which is an example of a suitable source of keying voltage in an electrical musical instrument such as an electronic organ.

A plurality of keys 18 (only a few of which are illustrated for purpose of simplification) are provided for connecting tone generator keyers 19 to a source of keying voltage. Each keyer 119 may typically comprise means for gating a musical tone signal from a musical tone signal source (not shown) to a keyer output in response to the application of a DC keying voltage, such as the device disclosed in U.S. Pat. No. 3,636,231 to Schrecongost et al. entitled DC KEYED SYNTHESIS ORGAN EMPLOYlNG AN INTEGRATED CIR- CUIT.

The outputs of the pulse generator 13 and the keydown detector 16 are connected to the inputs of an OR gate or other suitable gating means 21 through leads 22 and 23 respectively. The pulse generator 13 and the key-down detector 16, the operation of which will be presently explained, are illustrated schematically in FIG. 2. The pulse generator 13 comprises the subject of a separate copending application Ser. No. 368,818, filed on June 11, 1973 in the names of A. F. Petrie and myself entitled PULSE GENERATOR FOR USE WITH AN ELECTRICAL MUSICAL INSTRU- MENT and assigned to the same assignee of record as the present application, the disclosure of which is hereby specifically incorporated by reference in this application.

The pulse generator 13, the key-down detector 16 and the OR gate 21 together comprise a switching means operable to produce a control voltage at a lead 24 in response to key playing. Playing any one of the keys 18 serves to cause a current to flow through the pulse generator 13 and the key-down detector 16; the pulse generator 13 produces at lead 22 a pulse illustrated at 26 of predetermined duration and amplitude (of approximately 28 volts), while the key-down detector produces a voltage output on lead 23 illustrated at 27 having a value approximately equal to the amplitude of the pulse 26, the voltage output 27 frequently having an undesirable component reflecting key bounce. The pulse generator 13 produces a pulse of predetermined duration greater than the possible key bounce time, whereby playing any of the keys produces at the output of the OR gate 21 a control voltage, illustrated at 28, having no component reflecting key bounce.

With additional reference to FIG. 2, in general, the pulse generator 13 comprises first and second transistors 29 and 31 in circuit with each other and having interconnected emitters, a resistor 32 or other sensing means connecting the voltage source at terminal 11 to the keys 18 (through lead 14-, the key-down detector 16 and lead 17) and the emitters, a capacitor 33 having a first terminal 34 connected to the voltage source 11, a resistor 36 for operatively connecting the second terminal 37 of said capacitor to ground potential, said second terminal 37 being connected to the base of transistor 29. Means are provided in circuit with the transistors 29 and 31 for biasing same to normally maintain transistor 29 in a conductive state and transistor 31 in a corresponding non-conductive state in response to said conductive state, conduction of transistor 29 causing voltage at terminal 37 to reach a first predetermined level. Playing any one of the keys 18 serves to operably reverse the respective state of each transistor in response to voltage drop across the resistor 32 only until voltage on the second terminal 37 changes after a predetermined time interval from said first level to a second predetermined level sufficient to reinitiate conduction of the first transistor 29, the pulse output being determined by the conduction time of transistor 31. Playing any one of the keys therefore actuates the pulse generator to produce a pulse of duration determined by the time required for voltage on terminal 37 to change from said first to said second level. The detailed operation of the pulse generator 13 appears in said copending application Ser. No. 368,818, which is incorporated herein by reference.

The key-down detector 16 comprises two transistors 41 and 42 connected as a Darlington amplifier, a bypass capacitor 43 (for transient voltages), and resistors 44 and 46. Transistors 41 and 42 are non-conducting when none of the keys 18 are played due to the absence of forward bias, and lead 23 is correspondingly at approximately 0 volts. When one or more of the keys are closed, the small current flow through resistor 44 provides sufficient forward bias on transistors 41 and 42 to conduct, with the result that the voltage on lead 23 becomes approximately 28 volts, corresponding to the amplitude of the pulse on lead 22, as lead 23 is then connected to the voltage source at terminal 11 through lead 12, the pulse generator 13, lead 14 and conducting transistor 42.

The repetitive keyer actuating circuit according to the present invention is operable in response to key playing to produce electrical keying pulses for alternately and repeatedly actuating two sets of keyers 19. Of course, only one such set of keyers may be repeatedly actuated, depending upon the musical effect desired. The repetitive keyer actuation circuit of the present invention comprises: a keying pulse generating means in circuit with the voltage source at terminal 11 and the keys 18 and operable in response to key playing to alternately and repeatedly provide at each of two outputskeying pulses at regular preselected time intervals, and keying pulse sustain circuits each in corresponding circuit arrangement with one of said outputs and a set of keyers and operable to produce multiple stage envelope decay for said keying pulses. Each set of keyers is actuated by an initially percussive and subsequently sustained keying pulse in order to provide good repeatable effects throughout the entire range of frequencies of the keying pulses.

The keying pulse generating means comprises an electronic oscillating means which, in the preferred embodiment, comprises a repeat oscillator 51(schematically illustrated in FIG. 3) connected in turn by means of a lead 52 to a conventional pulse amplifier 53, said oscillating means being connected both to said switching means by means of lead 24 and to a conventional bistable keying multivibrator by means of a lead 54. The multivibrator 56 comprises first and second outputs 57 and 58 whereby only corresponding one of said outputs is energized in each of the two operating states of said multivibrator. The oscillating means is operable in response to the presence of a control voltage on lead 24 to produce a series of multivibrator triggering pulses on lead 54 of preselected frequency for reversing the operating states of the multivibrator. The repeat oscillator 51 comprises a conventional uni junction transistor oscillator operable in a well-known manner to produce at a preselected rate determined by the setting of a variable resistor 59 pulses which are amplified by the pulse amplifier 53 for triggering the keying multivibrator 56.

It should be noted that the voltages and component values illustrated in the figures correspond to those voltages and component values typically utilized in a working embodiment of the present invention, but operation of the repetitive keyer actuating circuit is certainly not restricted to those values shown, their selection being merely a matter of design choice.

The keying pulse generating means further comprises a control lead 71 connecting the output of said switch ing means at terminal 2 1- with said multivibrator 56 for setting same into a predetermined one of its two operating states by means of the control voltage on lead 28 notwithstanding operation of said oscillating means. As the multivibrator 56 remains in the state in which it was operating when the last key was released, it is desirable to initially start the multivibrator in a predetermined one of its operating states, for the reason which will become presently apparent. An OR gate or other gating means 72 is further provided having respective inputs thereof comprising the first output 57 of the multivibrator 56 and a lead 73 which in turn is connected to lead 24 by means of a lead 74 and an inverter 76.

The keying pulse generating means also comprises first and second output stagesor drivers 77 and 78, the input of the second output stage 78 being connected to the second multivibrator output 58, and the input of the first output stage 77 being connected to the output of the OR gate 72 by means of a lead 79. Each output stage 77 and 78, which is typically illustrated in the schematic diagram of FIG. 4 is in turn in circuit with a corresponding one of the sets of keyers 19 and operable in response to predetermined change in energization of its respective input to produce a pulse for actuating said keyer set.

The first output stage 77 is connected by means of a lead 81 to a repeat sustain circuit and amplifier 82 which, in turn, is connected by means of a lead 83, a mode selector switch 84 and a lead 86 to a first set of keyers (represented in FIG. 1 by only one keyer 19). Similarly, the second output stage 78 is connected by means-of a lead 87, to an alternate repeat sustain circuit and amplifier 88 which, in turn, is connected by means of a lead 91, the mode selector switch 84 and a lead 92 to a second or alternate set of keyers (also represented by one keyer 19). In the operation of the repetitive keyer actuating circuit, it is desirable for the first output stage 77 to actuate its corresponding set of keyers prior to the actuation of the second or alternate group of keyers by the second output stage 78, in order to properly simulate the desired musical sound. Key playing serves to actuate the first and second output stages 77 and 78 beginning with the first output stage 77 to produce electrical keying pulses for alternately and repeatedly actuating the first'and second sets of keyers at equal preselected intervals.

As noted earlier, the control lead 71 connects the output of the switching means at lead 2 1 to the multivibrator 56 for setting same into predetermined one of its operating states by means of the control voltage on lead 24 notwithstanding operation of the oscillating means. The multivibrator 56 is accordingly set to the operating state where its' first output 57 is at volts upon key playing, if the multivibrator is not already in that state as a result of prior key playing and release thereof. With reference to FIG. 41, positive-going changes at outputs 58 and 79 are operable, when differentiated by capacitor 93 and resistor 95, to turn on in a well known manner the normally non-conducting transistor 94 to produce a negativegoing keying pulse in a well known manner. When the keying multivibrator is already in the state wherein its first input 57 is a 0 volts, the OR gate 72 insures initial operation of the first output stage 77 upon key playing by providing at lead 79 a positivegoing pulse obtained by inverting the control voltage represented at 28; it is seen that the output of the OR gate provides a positive-going change in energization on lead 79 to the input of the first output stage or driver 77 in response to either the positive-going change in energization of the first multivibrator output 57 (from a negative voltage to O), or in response to the control voltage when the multivibrator is in that predetermined state (0 volts at output lead 57) prior to key playing, as the case may be. It is seen that key playing serves to actuate the first and second output stages 77 and 78 beginning with the first output stage 77 to produce electrical keying pulses for alternately and repeatedly actuating the first and second sets of keyers at equal time intervals due to the operation of the bistable multivibrator 56.

FIG. Sillustrates schematically the sustain circuit and amplifier (typical of 82 and 89) forming the subject of my said copending application which is here used in conjunction with the key pulse generating means just disclosed in order to provide initially percussive and subsequently sustained keying pulses for actuating the tone generator keyers. The operation of the sustain circuit for producing multiple stage envelope decay is described in detail in my said copending application Ser. No. 368,878. In general, however, the sustain circuits 82 and 89 each comprise a capacitor 181 charged by each applied keying pulse to a first voltage of approximately l4 volts, a first resistance path comprising resistor 182 of relatively low value for discharging said capacitor to a second voltage at terminal 183 having a value intermediate ground potential and l4 volts determined by the voltage divider comprising resistances 184i and 186, and a second resistor 187 (of relatively high value) for discharging said capacitor 181 to ground potential. Resistor 182 is provided with a diode 188 in circuit therewith for enabling capacitor 181 to discharge to the second or intermediate voltage and for preventing reverse current flow through the resistor 182 when the capacitor voltage decreases below the intermediate voltage. Decaying voltage waveform envelopes are formed in multiple stages in accordance with the discharge rates of capacitor 181 through the first and second paths, said rates having unlike time con stants. Resistor 189 is provided to control the pulse rise time. A conventional Darlington amplifier comprising transistors 111 and 112 is further provided to amplify the keying pulses.

The mode selector switch 84 is provided to selectively connect leads 86 and 92 to the repetitive keyer actuating circuit in the repeat mode or to another keying voltage source (not shown) in the non-repeat mode as desired.

I claim:

1. In an electrical musical instrument of the keyboard type having a plurality of selectively orperated keyswitches for connecting corresponding tone generator keyers to a source of keying voltage, a repetitive keyer actuating circuit operable in response to keyswitch actuation to produce electrical keying pulses for alternately and repeatedly actuating two sets of keyers, comprising: keying pulse generating means coupled between said source of keying voltage and said key-switches for alternately and repeatedly producing pulses on each of two output signal leads in response to actuation of at least one of said keyswitches; and a pair of sustain circuit means each coupled between an associated one of said output signal leads and an associated set of keyers ,7 for producing a keying pulse envelope having a multiple stage decay; whereby each set of keyers is actuated by an initially percussive and subsequently sustained keying pulse.

2. Apparatus as claimed in claim 1, wherein said pulse generating means comprises:

switching circuit means coupled between said source of keying voltage and said keyswitches for producing a control signal in response to actuation of at least one keyswitch;

oscillator circuit means for producing a repetitive series of pulses in response to said control signal;

abistable multivibrator circuit for producing alternating pulses on first and second output leads in response to said repetitive series of pulses;

a control lead connected between said switching circuit means and said multivibrator circuit for setting said multivibrator into a preselected state upon initial appearance of said key-down signal;

a first output circuit coupled between said first output lead and a first one of said sustain circuit means for operating said first set of keyers in response to a pulse on said first output lead, and including gating means coupled to said switching circuit means for initially operating said first set of keyers regardless of the initial state of said multivibrator circuit; and

a second output circuit coupled between said second output lead and a second one of said sustain circuit means for operating said second set of keyers in response to a pulse on said second output lead.

3. Apparatus as claimed in claim 2, wherein said switching circuit means comprises:

. pulse generator circuit means for producing a pulse of predetermined duration and amplitude in response to actuation of at least one of said key switches;

key-down detector circuit means for producing a key-down signal of amplitude substantially equal to said amplitude of said pulse in response to actuation of at least one of said keyswitches, said keydown signal having a parasitic component reflecting keyswitch bounce; and

an OR gate coupled to said pulse generator circuit means and said key-down detector circuit means for producing said control signal in response to at least one of said pulse and said key-down signal; said duration of said pulse being greater than the key-bounce time, whereby said control voltage has no parasitic component due to key-bounce.

4. Apparatus as claimed in claim 2, wherein said oscillator circuit means comprises a unijunction transistor oscillator and a pulse amplifier coupled to the output of said oscillator.

5. Apparatus as claimed in claim 2, wherein said gating means comprises an OR gate.

6. In an electrical musical instrument of the keyboard type having a plurality of selectively operated keyswitches for connecting corresponding tone generator keyers to a source of keying voltage, switching circuit means for producing a control signal in response to keyswitch actuation comprising: pulse generator circuit means coupled between said source of keying voltage and said keyswitches for producing a pulse of predetermined duration and amplitude in response to actuation of at least one of said keyswitches; key-down detector circuit means coupled between said source of keying voltage and said keyswitches for producing a key-down signal of amplitude substantially equal to said amplitude of said pulse from said pulse generator circuit means in response to actuation of at least one of said keyswitches, said key-down signal having a parasitic component reflecting keyswitch bounce; and an OR gate having inputs coupled to said pulse generator circuit means and said key-down detector circuit means for producing said control signal in response to at least one of said pulse and said key-down signal; said duration of said pulse being greater than the key-bounce time, whereby said control voltage has no parasitic component due to key-bounce.

7. In an electrical musical instrument of the keyboard type having a plurality of selectively operated keyswitches for connecting corresponding tone generator keyers to a source of keying voltage, a repetitive keyer actuating circuit operable in response to keyswitch actuation to produce electrical keying pulses for alternately and repeatedly actuating two sets of keyers comprising:

switching circuit means coupled between said source of keying voltage and said keyswitches for producing a control signal in response to actuation of at least one keyswitch;

oscillator circuit means for producing a repetitive series of pulses in response to said control signal;

a bistable multivibrator circuit for producing alternating pulses on first and second output leads in response to said repetitive series of pulses;

a control lead connected between said switching circuit means and said multivibrator circuit for setting said multivibrator into a preselected state upon initial appearance of said key-down signal;

a first sustain circuit means coupled between said first output lead and an associated first set of keyers for producing a percussion-sustain keying signal to operate said first set of keyers in response to pulses on said first output lead;

a second sustain circuit coupled between said first output lead and an associated second set of keyers for producing a percussion-sustain keying signal to operate said first set of keyers in response to pulses on said second output lead; and

a gating means coupled between said switching cir-' cuit means and said first sustain circuit to cause operation of said first set of keyers upon initial keyswitch actuation regardless of the initial operating state of said multivibrator circuit.

8. Apparatus as claimed in claim 7, wherein said switching circuit means comprises:

pulse generator circuit means for producing a pulse of predetermined duration and amplitude in response to actuation of at least one of said key switches;

key-down detector circuit means for producing a key-down signal of amplitude substantially equal to said amplitude of said pulse in response to actuation of at least one of said keyswitches, said keydown signal having a parasitic component reflecting keyswitch bounce; and

an OR gate coupled to said pulse generator circuit means and said key-down detector circuit means for producing said control signal in response to at least one of said pulse and said key-down signal; said duration of said pulse being greater than the key-bounce time, whereby said control voltage has put of said oscillator. no parasitic component due to key-bounce. 9. Apparatus as claimed in claim 7, wherein said oscillator circuit means comprises a unijunction transisgatmg means compnses an OR gate' tor oscillator and a pulse amplifier coupled to the out- Ill). Apparatus as claimed in claim 7, wherein said 

1. In an electrical musical instrument of the keyboard type having a plurality of selectively orperated keyswitches for connecting corresponding tone generator keyers to a source of keying voltage, a repetitive keyer actuating circuit operable in response to keyswitch actuation to produce electrical keying pulses for alternately and repeatedly actuating two sets of keyers, comprising: keying pulse generating means coupled between said source of keying voltage and said key-switches for alternately and repeatedly producing pulses on each of two output signal leads in response to actuation of at least one of said keyswitches; and a pair of sustain circuit means each coupled between an associated one of said output signal leads and an associated set of keyers for producing a keying pulse envelope having a multiple stage decay; whereby each set of keyers is actuated by an initially percussive and subsequently sustained keying pulse.
 2. Apparatus as claimed in claim 1, wherein said pulse generating means comprises: switching circuit means coupled between said source of keying voltage and said keyswitches for producing a control signal in response to actuation of at least one keyswitch; oscillator circuit means for producing a repetitive series of pulses in response to said control signal; a bistable multivibrator circuit for producing alternating pulses on first and second output leads in response to said repetitive series of pulses; a control lead connected between said switching circuit means and said multivibrator circuit for setting said multivibrator into a preselected state upon initial appearance of said key-down signal; a first output circuit coupled between said first output lead and a first one of said sustain circuit means for operating said first set of keyers in response to a pulse on said first output lead, and including gating means coupled to said switching circuit means for initially operating said first set of keyers regardless of the initial state of said multivibrator circuit; and a second output circuit coupled between said second output lead and a second one of said sustain circuit means for operating said second set of keyers in response to a pulse on said second output lead.
 3. Apparatus as claimed in claim 2, wherein said switching circuit means comprises: pulse generator circuit means for producing a pulse of predetermined duration and amplitude in response to actuation of at least one of said key switches; key-down detector circuit means for producing a key-down signal of amplitude substantially equal to said amplitude of said pulse in response to actuation of at least one of said keyswitches, said key-down signal having a parasitic component reflecting keyswitch bounce; and an OR gate coupled to said pulse generator circuit means and said key-down detector circuit means for producing said control signal in response to at least one of said pulse and said key-down signal; said duration of said pulse being greater than the key-bounce time, whereby said control voltage has no parasitic component due to key-bounce.
 4. Apparatus as claimed in claim 2, wherein said oscillator circuit means comprises a unijunction transistor oscillator and a pulse amplifier coupled to the output of said oscillator.
 5. Apparatus as claimed in claim 2, wherein said gating means comprises an OR gate.
 6. In an electrical musical instrument of the keyboard type having a plurality of selectively operated keyswitches for connecting corresponding tone generator keyers to a source of keying voltage, switching circuit means for producing a control signal in response to keyswitch actuation comprising: pulse generator circuit means coupled between said source of keying voltage and said keyswitches for producing a pulse of predetermined duration and amplitude in response to actuation of at least one of said keyswitches; key-down detector circuit means coupled between said source of keying voltage and said keyswitches for producing a key-down signal of amplitude substantially equal to said amplitude of said pulse from said pulse generator circuit means in response to actuation of at least one of said keyswitches, said key-down signal having a parasitic component reflecting keyswitch bounce; and an OR gate having inputs coupled to said pulse generator circuit means and said key-down detector circuit means for producing said control signal in response to at least one of said pulse and said key-down signal; said duration of said pulse being greater than the key-bounce time, whereby said control voltage has no parasitic component due to key-bounce.
 7. In an electrical musical instrument of the keyboard type having a plurality of selectively operated keyswitches for connecting corresponding tone generator keyers to a source of keying voltage, a repetitive keyer actuating circuit operable in response to keyswitch actuation to produce electrical keying pulses for alternately and repeatedly actuating two sets of keyers comprising: switching circuit means coupled between said source of keying voltage and said keyswitches for producing a control signal in response to actuation of at least one keyswitch; oscillator circuit means for producing a repetitive series of pulses in response to said control signal; a bistable multivibrator circuit for producing alternating pulses on first and second output leads in response to said repetitive series of pulses; a control lead connected between said switching circuit means and said multivibrator circuit for setting said multivibrator into a preselected state upon initial appearance of said key-down signal; a first sustain circuit means coupled between said first output lead and an associated first set of keyers for producing a percussion-sustain keying signal to operate said first set of keyers in response to pulses on said first output lead; a second sustain circuit coupled between said first output lead and an associated second set of keyers for producing a percussion-sustain keying signal to operate said first set of keyers in response to pulses on said second output lead; and a gating means coupled between said switching circuit means and said first sustain circuit to cause operation of said first set of keyers upon initial keyswitch actuation regardless of the initial operating state of said multivibrator circuit.
 8. Apparatus as claimed in claim 7, wherein said switching circuit means comprises: pulse generator circuit means for producing a pulse of predetermined duration and amplitude in response to actuation of at least one of said key switches; key-down detector circuit means for producing a key-down signal of amplitude substantially equal to said amplitude of said pulse in response to actuation of at least one of said keyswitches, said key-down signal having a parasitic component reflecting keyswitch bounce; and an OR gate coupled to said pulse generator circuit means and said key-down detector circuit means for producing said control signal in response to at least one of said pulse and said key-down signal; said duration of said pulse being greater than the key-bounce time, whereby said control voltage has no parasitic component due to key-bounce.
 9. Apparatus as claimed in claim 7, wherein said oscillator circuit means comprises a unijunction transistor oscillator and a pulse amplifier coupled to the output of said oscillator.
 10. Apparatus as claimed in claim 7, wherein said gating means comprises an OR gate. 